Studies in fluorescence histochemistry: III. The demonstration with salicylhydrazide of the aldehydes present in periodate‐oxidized mucosubstances *

SYNOPSIS Salicylhydrazide forms blue fluorescent derivatives with all potentially Schiff‐reactive, periodate‐oxidized mucosubstances in sections of fixed tissue. The derivatives formed from sulpho‐ and sialomucins usually emit an intense fluorescence. The fluorescence emitted by neutral mucosubstance derivatives is less intense. Aluminium salts enhance the fluorescence emitted by these derivatives, but zinc salts tend to quench it. Salicylhydrazide forms stable fluorescent products only with aldehydes, and is therefore highly specific. Moreover, its aldehyde hydrazones are unique among aldehyde acid arylhydrazones in that only they can be converted into formazans. Cytoplasmic proteins emit a red or purple fluorescence after being treated with a solution containing a solochrome black dye and an aluminium salt. This fluorescence enables the blue fluorescence emitted by periodate‐oxidized mucosubstance salicylhydrazones to be seen more clearly.